The present invention is related generally to laser machines used for welding and machining of articles, and specifically to device that assures protection for portions of an article adjacent to the work area, such as a turbine airfoil, undergoing an operation by a laser machine from damage as a result of the by-products of the operation or from malfunction of the laser machine and a method for assuring that portions of the article are protected prior to and during an operation.
Laser machines are commonly used for welding and machining of articles. In the modern manufacturing environment, this equipment is used with increasing frequency in situations in which precision is required and speed is important. This equipment can be used to lower costs by increasing output while reducing rates of scrap.
These laser machines are increasingly used for manufacturing operations in which large numbers of identical parts must be made with great precision, and the costs of the materials for such parts is high, so that scrappage of the parts is undesirable. Because of the repetitive nature of these precision operations, these laser machines typically include well-known controllers that can be programmed to perform a series of operations with minimum input by the operator. One area in which these laser machines have found use is in the manufacture of airfoils for gas turbine engines. These airfoils are expensive, intricate articles that usually are manufactured to near final form by investment casting. Not only is the casting process expensive, but the airfoils can be made of expensive superalloy material or titanium alloy material. However, because of the intricacy of these airfoils, it is not possible for the investment casting operations to always provide a finished product. For example, it may be necessary to drill fine holes through the airfoils, or to provide a fluid connection from a passageway manufactured into the airfoil by the investment casting process to the airfoil surface. Alternatively, it may be necessary to add a different material to the airfoil surface. This cannot be accomplished by casting, but can readily be accomplished by laser welding. It may also be desirable to refurbish an airfoil removed from service or damaged during a manufacturing operation by repair welding. This can be accomplished using the same material as the base material, or material different than the original base material.
One of the problems with all types of the operations performed by a laser machine is the possibility of collateral damage to the regions of the article immediately adjacent to the area undergoing the operation, whether the operation is a machining operation or a welding operation. Some material being removed from or added to the article can be ejected from the work area and deposited on an adjacent area. Additionally, the laser beam may be reflected onto the adjacent area and may cause damage to the adjacent region. The laser nozzle itself may overshoot its target area or be misaligned, and the adjacent region may be damaged. The laser beam can also cause damage to portions of the workpiece beneath, on the underside or on the opposite side of the work area
The most effective method, particularly for airfoil applications, has been for the laser operator to position laser beam stop material onto the airfoil on the regions adjacent to the area that is to be processed. However, due to the fast pace of the manufacturing environment, it is not uncommon after the application of the laser beam stop material that the material is either forgotten during the processing, or is moved out of position inadvertently during the processing. While the failure to place the laser beam stop material into position may not always be catastrophic, that is resulting in the need to scrap the article, it can result in damage that, while repairable, is expensive and time-consuming, usually requiring delicate hand-working operations.
Therefore, what is needed is an effective and reliable method that can prevent operator error by assuring that the laser beam stop material is in position to prevent collateral damage to areas adjacent to that undergoing repair. This method can best be accomplished by modifications to the laser machine and process.
A method for protecting or safeguarding from collateral damage portions of a workpiece adjacent to the area undergoing laser operations is set forth. The collateral damage is attributable to the effects of laser processing, and can be the result of laser beam reflection onto the adjacent area, back wall burn as a result of the laser beam penetrating the work area and projecting onto an underlying surface of the workpiece, or can be the result of molten material ejected from the region undergoing the laser operation. It can simply be the result of improper functioning of the machine causing it to deviate from its intended path, or from improper positioning of the fixture holding the workpiece in relation to the laser nozzle or improper location of the workpiece in the fixture.
A laser machine that includes a laser nozzle assembly is provided to accomplish the laser operations. The laser operations can include laser welding operations or laser machining operations, such as controlled drilling of laser holes. The laser machine includes a programmable controller that controls the operations of the laser machine and laser nozzle. The controller controls the operation of the machine by sending and receiving signals to initiate and terminate tasks. These tasks are included in a program that is programmed into the controller by an operator. The laser machine also includes a table having a motion system that moves in response to instructions from the controller. The program directs the laser machine, including the movable table, and the laser nozzle assembly to perform a sequence of operations to execute preselected tasks at predetermined locations on the workpiece to accomplish a desired result, such as depositing material to a predetermined thickness or drilling a hole of specified dimensions at a specified location.
The workpiece is typically provided in a fixture. The fixture is used to position the workpiece in spatial relation to the laser nozzle on the laser table. Each operation that is to be performed on the workpiece may require a different fixture, as the spatial relationship may change. As the workpiece is placed into position in the fixture and the fixture is placed into position on the table relative to the laser nozzle but before the laser beam is activated, a beam stop material is placed over the workpiece to shield regions adjacent to the areas which are to undergo the laser operations, thereby affording these regions protection from the various undesirable collateral effects that can result from a laser operation, as previously set forth.
In the present invention, a sensor is provided to sense the presence or absence of beam stop material. The sensor is attached to the laser nozzle so that the sensor has a fixed spatial relationship with respect to the nozzle. Furthermore, the sensor is attached so that it will move as the laser nozzle moves. The program that directs the laser machine and the laser nozzle assembly to perform the sequence of operations is then executed. One of the operations in the sequence of operations programmed into the controller directs the laser nozzle to move to a preselected position. Upon moving the laser nozzle to a preselected position, the sensor, which also moves with the nozzle, detects the presence or absence of the beam stop material at the preselected locations of the workpiece adjacent to the location or locations at which operations are to be performed. If the beam stop material is present at the preselected location or locations, a signal is generated by the sensor and sent to the controller. At this point, the program is in a decision mode. In response to a signal from the sensor indicating the presence of the beam stop material in the appropriate location, the program provides instructions to the controller to execute the required sequence of operations. If a signal is not received from the sensor, the program remains in a holding pattern awaiting a positive response from the sensor. If no signal is received, the program does not provide the instructions required to execute the required sequence of operations.
An advantage of the present invention is that the reliance on the laser operator is no longer required to assure the proper placement of the beam stop material prior to initiation of the work operation.
Another advantage of the present invention is that the failure of the laser operator to properly place the beam stop material into position over the regions adjacent to the work area or the failure of the laser operator or properly position the beam stop at the correct location will prevent the laser operations from proceeding. The fail-safe nature of the process will also allow, indeed require, the laser operator to properly locate the beam material in position before the laser operations can proceed.
Still another advantage of the present invention is that collateral damage to regions adjacent to the work area will be prevented. As a result, time consuming and expensive hand rework operations will be reduced or eliminated, and scrap rates of expensive parts such as airfoils will be reduced.